fix(api): correct async self-invoke payload shape so collection actually runs

[cristim]

Summary

The async refresh path landed in #260 but the Lambda self-invoke payload doesn't match what the receiving Lambda's ParseScheduledEvent accepts. Every async invoke is being rejected, so the user clicks Refresh, the frontend polls indefinitely, and collection never actually runs — exact same UX as the original 60s timeout.

Evidence (deployed log group /aws/lambda/cudly-dev-426fc8af-api)

16:49:40 Received unknown event (size: 37 bytes)
16:49:40 Unknown event type, treating as scheduled event
16:49:40 {"errorMessage":"failed to parse scheduled event:
              unknown scheduled task action: \"\""}

37 bytes = the {"event":"scheduled_recommendations"} string exactly. The handler's ScheduledEvent struct has no event field — it has Action, Source, DetailType, Detail — so Action unmarshals as "" and the dispatch switch hits default → unknown scheduled task action.

Fix

Send the payload the dispatcher accepts:

{"source": "aws.events", "action": "collect_recommendations"}

action="collect_recommendations" maps to TaskCollectRecommendations in internal/server/handler.go::ParseScheduledEvent. source="aws.events" makes detectLambdaEventType in internal/server/lambda.go (which checks Source == "aws.events" || Action != "") classify it consistently with EventBridge cron deliveries.

Test plan

• go build ./... succeeds
• go test ./internal/api/... — 1,055 tests pass
• Pre-commit hooks all pass
• CI green on push
• After merge + redeploy, click Refresh on /recommendations and confirm:
  • Lambda log shows collect_recommendations task running (not the rejection error)
  • Frontend banner clears once last_collection_started_at clears
  • Recommendations list shows monthly_cost values populated for newly-collected rows

Why this didn't surface during PR #260's CI

CI runs Go unit tests with mocked Lambda invokers, so the payload shape was never end-to-end exercised against the receiving Lambda. The mismatch only manifests in the deployed environment when the real lambda.Invoke delivers the event back to the Lambda runtime.

Closes the user-visible symptom that re-opened the parent investigation under #257.

Summary by CodeRabbit

• Chores
  • Updated internal scheduler event handling to improve system reliability.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: a3d15d62-6a78-4490-a737-ede65c422d98

📥 Commits

Reviewing files that changed from the base of the PR and between 7eb77d1 and f5ff0c0.

📒 Files selected for processing (1)

• internal/api/handler_recommendations_refresh.go

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📝 Walkthrough

Walkthrough

The scheduler Lambda's self-invocation payload is reformatted from { "event": "scheduled_recommendations" } to { "source": "aws.events", "action": "collect_recommendations" } to align with receiving-side dispatch logic. Inline comments are updated to document the expected payload structure.

Changes

Scheduler Payload Update

Layer / File(s)	Summary
Payload Definition & Comments internal/api/handler_recommendations_refresh.go (lines 142–162)	asyncInvokeSelf builds the invoke payload with source: "aws.events" and action: "collect_recommendations". Comments updated to describe how the receiving side classifies and dispatches scheduled tasks based on source/action fields, noting that the prior event field payload is now rejected.
Invocation Wiring internal/api/handler_recommendations_refresh.go (lines 164–170)	Lambda invoke call remains unchanged in mechanism (InvocationTypeEvent, Payload field); only the payload contents passed to this call were updated.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

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🐰 A payload once old, now takes new shape,
With source and action in their place,
The scheduler hops along with glee,
Recommendations flow more gracefully! ✨

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately summarizes the main change: correcting the async self-invoke payload shape to fix recommendation collection execution.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/async-self-invoke-payload

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[cristim]

@coderabbitai full review

[coderabbitai]

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